"Power supply has been disrupted in seven states from 2.32 a.m. It has been partially affected in Delhi and Rajasthan. We are in the process of restoring the supply," V.V. Sharma, general manager of Power System Operation Corporation Limited, told IANS.

According to the Power System Operation Corp. Ltd., the exact reasons for the grid failure are being ascertained.

"The trouble resulted in power outage in the entire northern region, but for parts of Badarpur in south Delhi, Narora and Simbhauli in Uttar Pradesh and Bhinma in Rajasthan," a statement said.

The minister also said it was difficult to pin point a particular reason for the failure - one of the worst in the decade. The last time such a massive disruption occurred was in 2001-02, he informed.

He said a three-member panel has been set up to look at the exact cause.

The Power System Operation Corp., a subsidiary of the state-run Power Grid Corporation of India, which manages the northern grid, said effort was under way to seek supplies from the eastern and the western regions, even as power to the railway system had been partially restored.

"The restoration of the grid may take a few more hours. The engineers have been trying to restore it since early morning. We are giving first priority to public services like hospitals and transport," Sharma added.

As a result of the power failure, Delhi Metro services were disrupted for more than two hours Monday. However, the service was resumed later.